No iOS 5 AirPlay mirroring button on iPad 2

I has upgraded my iPad 2 to iOS 5, and upgraded iTunes to the latest version on my Mac. My Apple TV 2nd also has been upgraded to the latest software. But there is no AirPlay mirroring button on iPad 2. The iPad connectes to the router via Wi-Fi, and the Mac connectes to the router via Ethernet. How to get the feature to work?* Try rebooting both the router and modem.* If you activate AirPlay and